System and method for determining changes of an optical fibre

ABSTRACT

The invention relates to a method for determining temperature, pressure, strain, or other changes of an optical fibre ( 250 ) having Fiber Bragg Grating (FBG) patterns provided in at least one portion (Portion  1 ) of said optical fibre ( 250 ), said optical fibre ( 250 ) being connected between a first detector arrangement ( 210 ) and a second detector arrangement ( 220 ), the method comprising the steps of: 
     emitting (s 410 ) light into said optical fibre ( 250 ) in a first direction (D 1 ) from said first detector arrangement ( 210 ), receiving reflections from said (FBG) patterns of such emitted light by said first detector arrangement ( 210 ), and processing said reflections for determining a current temperature change related to said optical fibre ( 250 ); 
     on the basis of predetermined criteria, emitting (s 440 ) light into said optical fibre ( 250 ) in an opposite, second, direction (D 2 ) from said second detector arrangement ( 220 ), receiving reflections from said (FBG) patterns of such emitted light by said second detector arrangement ( 220 ), and processing said reflections for determining a current temperature change related to said optical fibre ( 250 ). 
     The invention relates also to a computer program product comprising program code (P) for a computer ( 233; 243; 253; 500 ) for implementing a method according to the invention. The invention relates also to a system ( 289 ) for determining temperature changes of an optical fibre ( 250 ). The invention also relates to a platform ( 100 ) being equipped with the system ( 289 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.17/647,190 filed Jan. 6, 2022, which is a continuation of U.S. patentapplication Ser. No. 16/269,776 filed Feb. 7, 2019, which claimspriority to Swedish Application No. 1850330-0 filed Mar. 23, 2018, thecontents of which are hereby incorporated herein in their entireties byreference.

TECHNICAL FIELD

The present invention relates to a method for determination oftemperature changes of an optical fibre. In particular the presentinvention relates to a method for determination of temperature changesof an optical fibre having Fiber Bragg Grating (FBG) patterns providedin at least one portion of said optical fibre, by means of the effectthe temperature change has on the wavelength reflected by the FBG. Theinvention relates also to a computer program product comprising programcode for a computer for implementing a method according to theinvention. It relates also to a system for determining temperaturechanges of an optical fibre having Fiber Bragg Grating (FBG) patternsand a platform being equipped with the system. The platform may be anaircraft, such as a commercial aircraft.

BACKGROUND ART

It is known to measure temperature changes along an optical fibre bymeans of Fibre Bragg Gratings. Hereby a plurality of Fibre BraggGratings are inscribed along the optical fibre. Each Fibre Bragg Gratingis active in its particular wavelength range within the electromagneticspectrum and reflects a certain narrow wavelength band, within theparticular wavelength range, depending on parameters like temperature,pressure, strain and indices of refraction. The reflected narrowwavelength band has a peak at the Bragg wavelength. A temperature changeresults in a shift of the peak wavelength. In order to avoiduncertainties regarding which Fibre Bragg Grating that contributes to acertain reflected peak wavelength, each Fibre Bragg Grating is given itsunique wavelength range.

One arrangement comprises a light source, detector and processing means,whereby one optical fibre is attached at one end to the arrangement.Hereby parameter changes may be detected and monitored. One suchparameter is temperature.

Aircrafts may be equipped with two such arrangements for sake ofredundancy. Hereby the arrangements are working in parallel. This is arather expensive solution because of the fact that the optical fibrecomprising Fibre Bragg Gratings is rather expensive.

SUMMARY OF THE INVENTION

There is a need to provide a robust and cost-effective system and methodfor determining temperature changes on-board e.g. an aircraft.

An object of the present invention is to propose a novel andadvantageous method for determining temperature changes of an opticalfibre.

Another object of the invention is to propose a novel and advantageoussystem and a novel and advantageous computer program for determiningtemperature changes of an optical fibre.

Another object of the present invention is to propose a novel andadvantageous method providing a more accurate and robust determinationof temperature changes of an optical fibre.

Another object of the invention is to propose a novel and advantageoussystem and a novel and advantageous computer program providing acost-effective determination of temperature changes of an optical fibre.

Yet another object of the invention is to propose a method, a system anda computer program achieving an automated, versatile and user friendlydetermination of temperature changes of an optical fibre.

Yet another object of the invention is to propose an alternative method,an alternative system and an alternative computer program fordetermination of temperature changes of an optical fibre.

Some of these objects are achieved with a method according to claim 1.Other objects are achieved with a system in accordance with what isdepicted herein. Advantageous embodiments are depicted in the dependentclaims. Substantially the same advantages of method steps of theproposed method hold true for corresponding means of the proposedsystem.

According to an aspect of the invention there is provided a method fordetermining temperature changes of an optical fibre having Fiber BraggGrating (FBG) patterns provided in at least one portion of said opticalfibre, said optical fibre being connected between a first detectorarrangement and a second detector arrangement, the method comprising thesteps of:

emitting light into said optical fibre in a first direction from saidfirst detector arrangement, receiving reflections from said (FBG)patterns of such emitted light by said first detector arrangement, andprocessing said reflections for determining a current temperature changerelated to said optical fibre;

on the basis of predetermined criteria, emitting light into said opticalfibre in an opposite, second, direction from said second detectorarrangement, receiving reflections from said (FBG) patterns of suchemitted light by said second detector arrangement, and processing saidreflections for determining a current temperature change related to saidoptical fibre.

Advantageously the proposed method may provide an accurately determinedtemperature change along the fibre. Hereby a cost-effective, automatedand user friendly method for determining a current temperature changerelated to said optical fibre is achieved.

The method may comprise the step of determining if said criteria isfulfilled.

The method may comprise the step of:

emitting light from said second detector arrangement if it is determinedthat said first detector arrangement is not operating properly and/or ifit is determined that a disconnection along said optical fibre is athand. These examples are relating to said criteria. Hereby a versatileand redundant method is achieved.

The method may comprise the step of:

operating only one of said first detector arrangement and said seconddetector arrangement; or

operating, in an alternating manner, said first detector arrangement andsaid second detector arrangement; or

operating both said first detector arrangement and said second detectorarrangement simultaneously. Hereby a versatile and flexible method isachieved. The proposed method is robust as down time of the system maybe reduced or minimized.

The method may comprise the step of:

determining a position of a temperature change along said optical fibreby performing a combined wavelength division multiplexing and timedivision multiplexing. By using a combined wavelength divisionmultiplexing and time division multiplexing a highly exact positionregarding said temperature change along the fibre may be determined.

The method may comprise the step of:

determining a temperature change course as a basis for a decisionregarding how to deal with said temperature change. Hereby acost-effective and reliable method is achieved. By extrapolatingtemperature changes on the basis of said determined course a mostdesired point of time for taking potential actions may be determined. Itmay for example be determined that the platform on which the proposedsystem is arranged, should be subject for immediate maintenance/serviceor that it is possible to wait for a more convenient and desired pointof time for performing required maintenance/service.

The method may comprise the step of:

providing a number of optical fibres having Fiber Bragg Grating (FBG)patterns provided in at least one portion of each of said opticalfibres, said optical fibres being connected between the first detectorarrangement and the second detector arrangement. Hereby a versatilemethod is achieved wherein various optical fibres may be arrangedwherever suitable within the platform.

The method may comprise the steps of:

detecting an identity of a certain optical fibre; and

determining a predetermined off-set characteristics related to the FiberBragg Grating (FBG) patterns of said certain optical fibre. Herebyaccuracy and reliability of the determined temperature changes isachieved.

According to an aspect of the invention there is provided a method fordetermining parameter changes of an optical fibre having Fiber BraggGrating (FBG) patterns provided in at least one portion of said opticalfibre, said optical fibre being connected between a first detectorarrangement and a second detector arrangement, the method comprising thesteps of:

emitting light into said optical fibre in a first direction from saidfirst detector arrangement, receiving reflections from said (FBG)patterns of such emitted light by said first detector arrangement, andprocessing said reflections for determining a current parameter changerelated to said optical fibre;

on the basis of predetermined criteria, emitting light into said opticalfibre in an opposite, second, direction from said second detectorarrangement, receiving reflections from said (FBG) patterns of suchemitted light by said second detector arrangement, and processing saidreflections for determining a current parameter change related to saidoptical fibre.

Said parameter may be e.g. pressure, strain or vibrations.

According to an aspect of the invention there is provided a method fordetermining parameter changes of an optical fibre having Fiber BraggGrating (FBG) patterns provided in at least one portion of said opticalfibre, said optical fibre being connected between a first detectorarrangement and a second detector arrangement, the method comprising thesteps of:

emitting light into said optical fibre in a first direction from saidfirst detector arrangement, receiving reflections from said (FBG)patterns of such emitted light by said first detector arrangement, andprocessing said reflections for determining a current parameter changerelated to said optical fibre;

emitting light into said optical fibre in an opposite, second, directionfrom said second detector arrangement, receiving reflections from said(FBG) patterns of such emitted light by said second detectorarrangement, and processing said reflections for determining a currentparameter change related to said optical fibre.

According to an aspect of the invention there is provided a system fordetermining temperature changes of an optical fibre having Fiber BraggGrating (FBG) patterns provided in at least one portion of said opticalfibre, the system comprising:

a first detector arrangement and a second detector arrangement whereinsaid first detector arrangement and second detector arrangement beingconnected by fibre;

means being arranged for emitting light into said optical fibre in afirst direction from said first detector arrangement, means beingarranged for receiving reflections from said (FBG) patterns of suchemitted light by said first detector arrangement, and means beingarranged for processing said reflections for determining a currenttemperature change related to said optical fibre;

means being arranged for, on the basis of predetermined criteria,emitting light into said optical fibre in an opposite, second, directionfrom said second detector arrangement, means being arranged forreceiving reflections from said (FBG) patterns of such emitted light bysaid second detector arrangement, and means being arranged forprocessing said reflections for determining a current temperature changerelated to said optical fibre.

The system may comprise:

means being arranged for emitting light from said second detectorarrangement if it is determined that said first detector arrangement isnot operating properly and/or if it is determined that a disconnectionalong said optical fibre is at hand

The system may comprise:

control means for operating said first detector arrangement and saidsecond detector arrangement in such a way that:

only one of said first detector arrangement and said second detectorarrangement is operating; or

said first detector arrangement and said second detector arrangement areoperating in an in an alternating manner; or

said first detector arrangement and said second detector arrangement areoperating simultaneously.

The system may comprise:

means being arranged for determining a position of a temperature changealong said optical fibre by performing a combined wavelength divisionmultiplexing and time division multiplexing.

The system may comprise:

means being arranged for determining a temperature change course as abasis for a decision regarding how to deal with said temperature change.

The system may comprise:

a number of optical fibres having Fiber Bragg Grating (FBG) patternsprovided in at least one portion of each of said optical fibres, whereinsaid number of optical fibres are arranged to be connected between thefirst detector arrangement and the second detector arrangement.

The system may comprise:

means being arranged for detecting an identity of a certain opticalfibre; and

means being arranged for determining a predetermined off-setcharacteristics related to the Fiber Bragg Grating (FBG) patterns ofsaid certain optical fibre.

According to an aspect of the invention there is provided a system fordetermining parameter changes of an optical fibre having Fiber BraggGrating (FBG) patterns provided in at least one portion of said opticalfibre, the system comprising:

a first detector arrangement and a second detector arrangement whereinsaid first detector arrangement and second detector arrangement beingconnected by fibre;

means being arranged for emitting light into said optical fibre in afirst direction from said first detector arrangement, means beingarranged for receiving reflections from said (FBG) patterns of suchemitted light by said first detector arrangement, and means beingarranged for processing said reflections for determining a currentparameter change related to said optical fibre;

means being arranged for, on the basis of predetermined criteria,emitting light into said optical fibre in an opposite, second, directionfrom said second detector arrangement, means being arranged forreceiving reflections from said (FBG) patterns of such emitted light bysaid second detector arrangement, and means being arranged forprocessing said reflections for determining a current parameter changerelated to said optical fibre.

According to an aspect of the invention there is provided a platformcomprising a system according to what is presented herein. According toan aspect of the invention there is provided a vehicle comprising asystem according to what is presented herein.

According to an aspect of the invention there is provided an aircraftcomprising a system according to what is presented herein.

The vehicle may be any from among a truck, bus or passenger car.

According to an aspect of the invention there is provided a computerprogram product comprising instructions which, when the program isexecuted by a computer, cause the computer to carry out any of the stepsof the method depicted herein.

According to an aspect of the invention there is provided acomputer-readable storage medium comprising instructions which, whenexecuted by a computer, cause the computer to carry out any of the stepsof the method depicted herein.

According to an aspect of the invention there is provided a computerprogram product comprising instructions which, when the program isexecuted by an electronic control arrangement, cause the electroniccontrol arrangement to carry out any of the steps of the method depictedherein.

According to an aspect of the invention there is provided acomputer-readable storage medium comprising instructions which, whenexecuted by an electronic control arrangement, cause the electroniccontrol arrangement to carry out any of the steps of the method depictedherein.

According to an aspect of the invention there is provided a computerprogram for determining temperature changes of an optical fibre havingFiber Bragg Grating (FBG) patterns provided in at least one portion ofsaid optical fibre, wherein the computer program comprises program codefor causing an electronic control arrangement or a computer connected tothe electronic control arrangement to perform anyone of the method stepsdepicted herein, when run on the electronic control arrangement or thecomputer.

According to an aspect of the invention there is provided a computerprogram for determining temperature changes of an optical fibre havingFiber Bragg Grating (FBG) patterns provided in at least one portion ofsaid optical fibre, wherein the computer program comprises program codestored on a computer-readable medium for causing an electronic controlarrangement or a computer connected to the electronic controlarrangement to perform anyone of the method steps depicted herein.

According to an aspect of the invention there is provided a computerprogram for determining temperature changes of an optical fibre havingFiber Bragg Grating (FBG) patterns provided in at least one portion ofsaid optical fibre, wherein the computer program comprises program codestored on a computer-readable medium for causing an electronic controlarrangement or a computer connected to the electronic controlarrangement to perform any one of the method steps depicted herein, whenrun on the electronic control arrangement or the computer.

According to an aspect of the invention there is provided a computerprogram product containing a program code stored on a computer-readablemedium for performing any one of the method steps depicted herein, whenthe computer program is run on an electronic control arrangement or acomputer connected to the electronic control arrangement.

According to an aspect of the invention there is provided a computerprogram product containing a program code stored non-volatile on acomputer-readable medium for performing any one of the method stepsdepicted herein, when the computer program is run on an electroniccontrol arrangement or a computer connected to the electronic controlarrangement.

Further objects, advantages and novel features of the present inventionwill become apparent to one skilled in the art from the followingdetails, and also by putting the invention into practice. Whereas theinvention is described below, it should be noted that it is not confinedto the specific details described. One skilled in the art having accessto the teachings herein will recognise further applications,modifications and incorporations in other fields, which are within thescope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For fuller understanding of embodiments of the present invention and itsfurther objects and advantages, the detailed description set out belowshould be read in conjunction with the accompanying drawings, in whichthe same reference notations denote similar items in the variousdiagrams, and in which:

FIG. 1 schematically illustrates a platform according to an embodimentof the invention;

FIG. 2 schematically illustrates a system according to an embodiment ofthe invention;

FIG. 3 schematically illustrates a an optical fibre;

FIG. 4a is a schematic flowchart of a method according to an embodimentof the invention;

FIG. 4b is a schematic flowchart of a method according to an embodimentof the invention; and

FIG. 5 schematically illustrates a computer according to an embodimentof the invention.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a platform 100. According to thisexample the platform is an aircraft. The aircraft may be a commercialcivil aircraft. The platform may be any suitable kind of aircraft, suchas a helicopter. The platform 100 comprises the proposed system 289,which is depicted in greater detail with reference to e.g. FIG. 2 below.

Herein the platform 100 may be any suitable vehicle being arranged withthe proposed system for determining temperature changes of an opticalfibre having Fiber Bragg Grating patterns provided in at least oneportion of said optical fibre

According to one embodiment the platform is a land vehicle comprising atractor unit and a trailer. The platform 100 may be a heavy vehicle,e.g. a truck or a bus. It may alternatively be a car. According to oneembodiment the platform may be a train.

The method and system are applicable to various vehicles, such as e.g. amining machine, tractor, dumper, wheel-loader, forest machine, earthmover, road construction vehicle, road planner, emergency vehicle or atracked vehicle.

The proposed method and the proposed system according to one aspect ofthe invention are well suited to other platforms than aircraft, e.g.watercraft. The watercraft may be of any kind, e.g. motorboats,steamers, ferries or ships.

The platform may be any suitable stationary facility, such as anapartment complex, house or office building.

The term “link” refers herein to a communication link which may be aphysical connection such as an opto-electronic communication line, or anon-physical connection such as a wireless connection, e.g. a radio linkor microwave link.

The term “control arrangement” is according to one embodiment hereindefined as an arrangement comprising only one electronic controlarrangement or a number of connected electronic control arrangements.Said one electronic control arrangement or said number of connectedelectronic control arrangements may be arranged to perform the stepsaccording to the method depicted herein.

Herein it is depicted that the proposed system is arranged to determinea temperature change along the optical fibre. I should however be notedthat the proposed system and method are applicable to detect changes ofa number of different parameters, such as pressure, vibrations,humidity, flow or strain.

FIG. 2 schematically illustrates a system 289 of the platform 100. Thesystem 289 is arranged in the platform 100.

A first detector arrangement 210 comprises a light emitting device 231.The light emitting device 231 is arranged to emit light (radiation) of apredetermined wavelength and bandwidth into an optical fibre 250. Thelight emitting device may be any suitable light source, such as asuperluminescent diode, laser emitting device or semiconductor opticalamplifier.

The optical fibre 250 comprises at least one portion of Fiber BraggGrating (FBG) patterns inscribed in the optical fibre. According to thisexample the optical fibre 250 comprises a first portion Portion 1 and asecond portion Portion X. The first portion Portion 1 comprises FiberBragg Grating (FBG) patterns. This is depicted in greater detail withreference to FIG. 3. The second portion Portion X does not comprise anyFiber Bragg Grating (FBG) patterns but is arranged to only transmit theprovided light. The optical fibre 250 is arranged between said firstdetector arrangement 210 and a second detector arrangement 220. Eachportion of the optical fibre 250 comprising the FBG patterns may be ofany suitable length, such as e.g. 1, 5 or 10 metres. According to oneembodiment the optical fibre comprises a number N of separated portions(Portion 1, . . . , Portion N). Each portion Portion 1-Portion N mayhereby be separated by a portion Portion X wherein no Fiber BraggGrating (FBG) patterns are provided.

According to one embodiment the second portion Portion X may beexcluded. Hereby there is provided an optical fibre 250 comprising FiberBragg Grating (FBG) patterns along the entire length of the opticalfibre 250. According to one embodiment FBG's may be equidistantlydistributed along the optical fibre 250. Hereby no delays between timedivision multiplexing time slots along the optical fibre 250 areprovided, contrary to typical systems having time division multiplexing(TDM). This may be achieved by the arrangement of selected wavelengthsin wavelength division multiplexing (WDM) along the elongation of theoptical fibre 250, in relation to the time division multiplexingarrangement.

The first detector arrangement 210 further comprises a light detectingdevice 232. The light detecting device 232 is arranged to receivereflected light (radiation) from the optical fibre 250. The lightdetecting device 232 is arranged to detect the received light from theoptical fibre. Hereby the light emitting device 231 is arranged to emitlight from said first detector arrangement 210 into the optical fibre250 in a first direction and the light detecting device 232 is arrangedto receive reflected light, which thus propagate in a second direction,opposite from said first direction.

The first detector arrangement 210 comprises a first control arrangement233. The first control arrangement 233 is arranged to control operationof said light emitting device 231 and said light detecting device 232.The first control arrangement is also arranged to perform spectralanalysis of the detected light so as to determine potential temperaturechanges along the optical fibre, i.e. along the portion (Portion 1) ofthe optical fibre 250 comprising the Fiber Bragg Grating patterns.

The second detector arrangement 220 comprises a similar set-up as thefirst detector arrangement 210 and is functioning in a similar way.

The second detector arrangement 220 comprises a light emitting device241. The light emitting device 241 is arranged to emit light (radiation)of a predetermined wavelength into an optical fibre 250. The lightemitting device 241 may be any suitable light source, such as asuperluminescent/superluminous diode (SLD), laser emitting device orsemiconductor optical amplifier.

The second detector arrangement 220 further comprises a light detectingdevice 242. The light detecting device 242 is arranged to receivereflected light (radiation) from the optical fibre 250. The lightdetecting device 242 is arranged to detect the received light from theoptical fibre 250. Hereby the light emitting device 241 is arranged toemit light from said second detector arrangement 220 into the opticalfibre 250 in said second direction and the light detecting device 242 isarranged to receive reflected light, which thus propagate in a firstdirection, opposite from said second direction.

The second detector arrangement 220 comprises a second controlarrangement 243. The second control arrangement 243 is arranged tocontrol operation of said light emitting device 241 and said lightdetecting device 242. The second control arrangement 243 is alsoarranged to perform spectral analysis of the detected light so as todetermine potential temperature changes along the optical fibre 250,i.e. along the portion (Portion 1) of the optical fibre 250 comprisingthe Fiber Bragg Grating patterns.

According to one embodiment the system 289 is operating by only usingthe first detector arrangement 210. This is referred to as normaloperation. Hereby the first detector arrangement 210 is functioning as a“Master” and the second detector arrangement is functioning as a“Slave”.

The first detector arrangement 210 and the second detector arrangement220 are arranged to determine if a predetermined criteria is fulfilled.Said criteria may relate to that said first detector arrangement 210 ismalfunctioning. Said criteria may relate to that there is the opticalfibre 250 is malfunctioning, such as a fibre break at any position alongthe first portion Portion 1.

According to one embodiment the first detector unit 210 and the seconddetector arrangement 220 are arranged for communication via a link L200.Hereby the first detector arrangement 210 may activate, when suitable,the second detector arrangement 220 for operation. This may be performedin case there is detected a break of the optical fibre 250.

According to one embodiment the second detector arrangement 220 mayactivate itself for operation. This may be performed in case the firstdetector arrangement 210 is malfunctioning.

In a case where there is a fibre break at a position of the firstportion Portion 1 both the first detector arrangement 210 and the seconddetector arrangement 220 may be operating, whereby the first detectorarrangement 210 is receiving reflections (in a second direction) fromFGB's up to said fibre break and the second detector arrangement 220 isreceiving reflections (in a first direction) from the from FGB's up tosaid fibre break.

According to one embodiment the first detector arrangement 210 and thesecond detector arrangement 220 may be operating in an alternatingmanner.

Both the first detector arrangement 210 and the second detectorarrangement 220 are arranged to determine a position of a temperaturechange along said optical fibre by performing a combined wavelengthdivision multiplexing and time division multiplexing. Hereby arelatively exact position of a detected temperature change may bedetermined.

Both the first detector arrangement 210 and the second detectorarrangement 220 are arranged to determining a temperature change courseas a basis for a decision regarding how to deal with said temperaturechange. By monitoring a temperature change along the optical fibre 250over time it may be determined if, and in that case when, any actionsare required to be taken. Hereby it may be determined if action isnecessary to be taken immediately or if actions may be taken at anysuitable occasion, such as at a point of time when maintenance orservice of the platform 100 is scheduled.

According to one embodiment a number M of optical fibres having FiberBragg Grating (FBG) patterns provided in at least one portion of each ofsaid optical fibres may be provided. Each of said optical fibres isconnected between the first detector arrangement 210 and the seconddetector arrangement 220. According to this embodiment the operation ofthe system 289 is performed in a similar way as when only one opticalfibre is provided. The different optical fibres may be independentlyarranged at the platform. The individual optical fibres may present aunique distribution of portions having Fiber Bragg Grating patterns. Theset-up of optical fibres may be changed, so as to connect more opticalfibres to the first detector arrangement 210 and the second detectorarrangement 220 or to disconnect one or more optical fibres from thefirst detector arrangement 210 and the second detector arrangement 220.Hereby a flexible system 289 is provided.

The first detector arrangement 210 and the second detector arrangement220 may be arranged to detect a unique identity of a certain opticalfibre of the system 289. Hereby each of the connected optical fibres isprovided with an array of FGB's whereby a corresponding identity may beread out from a spectral analysis performed by the first detectorarrangement 210 and/or the second detector arrangement 220. According tothis embodiment the first detector arrangement 210 and/or the seconddetector arrangement 220 have pre-stored information regarding off-setcharacteristics related to the Fiber Bragg Grating patterns of saidcertain optical fibre. The off-set characteristics may hereby be used soas to determine temperature changes along the optical fibre in a moreaccurate way.

A third control arrangement 253 is arranged for communication with thefirst detector arrangement 210 via a link L210. The third controlarrangement 253 is arranged for communication with the second detectorarrangement 220 via a link L220. It may be releasably connected to thefirst detector arrangement 210 and the second detector arrangement 220.It may be a control arrangement external to the platform 100. It may beadapted to performing the steps according to embodiments of theinvention. It may be used to cross-load software to the first detectorarrangement 210 and the second detector arrangement 220, particularlysoftware for applying the method. It may alternatively be arranged forcommunication with the first detector arrangement 210 and the seconddetector arrangement 220 via an internal network on board the platform.It may be adapted to performing functions corresponding to those of thefirst detector arrangement 210 and the second detector arrangement 220,such as operating the first detector arrangement 210 only, the seconddetector arrangement 220 only, or both the first detector arrangement210 and the second detector arrangement 220 simultaneously.

According to one example the proposed method and system are used fordetecting hot air leakage from bleed air ducts of aircrafts. This is animplementation which is desirable especially considering theheat-sensitivity of composite materials commonly used inaero-structures.

The proposed systems advantageously achieves a configuration ofrelatively small weight.

FIG. 3 schematically illustrates an optical fibre 250 having Fiber BraggGrating patterns provided in a first portion Portion 1 and a secondportion Portion 2 of said optical fibre 250.

The optical fibre 250 may have any number of portions having Fiber BraggGrating patterns. The portions having Fiber Bragg Grating patterns areseparated by portions Portion X where no Fiber Bragg Grating patternsare provided. Each portion having Fiber Bragg Grating patterns may be ofany suitable length, such as 10, 50 or 100 meters, or more. The FGB's ineach portion may be separated by any suitable distance, such as forexample 2.0 cm.

By performing a combined wavelength division multiplexing and timedivision multiplexing by means of e.g. the first control arrangement 231it may be determined which unique FGB is subjected to a temperaturechange. By performing a combined wavelength division multiplexing andtime division multiplexing by means of e.g. the first controlarrangement 231 it may be determined which unique FGB is subjected to aparameter change, e.g. a pressure change, strain change, or other.

According to one embodiment the total lengths of the portions havingFiber Bragg Grating patterns constitutes less than 50% of the totallength of the optical fibre 250. According to one embodiment the totallengths of the portions having Fiber Bragg Grating patterns constitutesless than 25% of the total length of the optical fibre 250. Thisadvantageously achieves a relatively cheap system.

According to one embodiment substantially the entire length of theoptical fibre is constituted of Fiber Bragg Grating patterns, meaningthat no portion Portion X is provided.

Advantageously the length of the core of the optical fibre is slightlylonger than the casing of the optical fibre. By configuring the opticalfibre in this way the risk for unwanted strain affecting the wavelengthsof the light reflected by the FGB's are reduced, minimized oreliminated. Hereby an accurate method and system according to an aspectis achieved.

FIG. 4a schematically illustrates a flow chart of a method fordetermining temperature changes of an optical fibre 250 having FiberBragg Grating (FBG) patterns provided in at least one portion Portion 1of said optical fibre 250, said optical fibre 250 being connectedbetween a first detector arrangement 210 and a second detectorarrangement 220. The method comprises a method step s401. The methodstep s401 comprises the steps of:

emitting light into said optical fibre 250 in a first direction D1 fromsaid first detector arrangement 210, receiving reflections from saidpatterns of such emitted light by said first detector arrangement 210,and processing said reflections for determining a current temperaturechange related to said optical fibre 250;

on the basis of predetermined criteria, emitting light into said opticalfibre 250 in an opposite, second, direction D2 from said second detectorarrangement 220, receiving reflections from said patterns of suchemitted light by said second detector arrangement 220, and processingsaid reflections for determining a current temperature change related tosaid optical fibre 250.

After the method step s401 the method ends/is returned.

FIG. 4b schematically illustrates a flow chart of a method fordetermining temperature changes of an optical fibre 250 having FiberBragg Grating patterns provided in at least one portion Portion 1 ofsaid optical fibre 250, said optical fibre 250 being connected between afirst detector arrangement 210 and a second detector arrangement 220.

The method comprises a method step s410. The method step s410 comprisesthe step of emitting light into said optical fibre 250 in a firstdirection D1 from said first detector arrangement 210, receivingreflections from said (FBG) patterns of such emitted light by said firstdetector arrangement 210, and processing said reflections fordetermining a current temperature change related to said optical fibre250. This is referred to as normal operation of the system 289, namelythat only the first detector arrangement 210 is operating.

After the method step s410 a subsequent method step s420 is performed.

The method step s420 comprises the step of determining if apredetermined criteria is fulfilled. The criteria may be that said firstdetector arrangement 210 is not operating properly and/or if it isdetermined that a disconnection along said optical fibre 250 is at hand.The criteria may be that said first detector arrangement 210 is shutdown for some reason. This may be performed by means of any one of saidfirst control arrangement 233, second control arrangement 243 or thirdcontrol arrangement 253. If the criteria is fulfilled a subsequentmethod step s430 is performed. If the criteria is not fulfilled, themethod step s410 is performed again.

The method step s430 comprises the step of determining operation of thesystem 289. The method step s430 may comprise the step of operating onlyone of said first detector arrangement 210 and said second detectorarrangement 220. Operating only the first detector arrangement 210 maybe performed as normal operation. Operating only the second detectorarrangement 220 may be performed if the first detector arrangement 210is malfunctioning.

The method step s430 may comprise the step of operating, in analternating manner, said first detector arrangement 210 and said seconddetector arrangement 220. This may be performed when it is desired toswitch operation between said first detector arrangement 210 and saidsecond detector arrangement 220.

The method step s430 may comprise the step of operating both said firstdetector arrangement 210 and said second detector arrangement 220simultaneously. This may be performed in a case when there is adisconnection somewhere along the optical fibre, e.g. at a positionwithin the first portion Portion 1.

In case operation is determined to involve operation of the seconddetector arrangement 220 a method step s440 is performed.

The method step s440 comprises the step of, on the basis ofpredetermined criteria, emitting light into said optical fibre 250 in anopposite, second, direction D2 from said second detector arrangement220, receiving reflections from said patterns of such emitted light bysaid second detector arrangement 220, and processing said reflectionsfor determining a current temperature change related to said opticalfibre 220.

After the method step s440 a method step s450 is performed.

The method step s450 comprises the step of determining a position of atemperature change along said optical fibre by performing a combinedwavelength division multiplexing and time division multiplexing. This isexplained in greater detail with reference to FIG. 3.

The method step s450 comprises the steps of:

detecting an identity of a certain optical fibre 250; and

determining a predetermined off-set characteristics related to the FiberBragg Grating (FBG) patterns of said certain optical fibre 250.

It should be noted that the steps of detecting an identity of a certainoptical fibre 250 and determining corresponding predetermined off-setcharacteristics may be performed at any suitable point of time, such asa first step of the proposed method or during a platform service event.

The relevant pre-stored off-set characteristics may be determined bymeans of said first control arrangement 233, said second controlarrangement 243 or said third control arrangement 253. Hereby theidentity of the optical fibre 250 is determined by means of a fibreunique Fiber Bragg Grating (FBG) pattern. Hereby off-set values for eachFBG of the identified fibre 250 are provided. The relevant off-setvalues may be used when determining a temperature change by the proposedmethod and system.

In case there is provided a number of optical fibres having Fiber BraggGrating (FBG) patterns provided in at least one portion of each of saidoptical fibres, said optical fibres being connected between the firstdetector arrangement 210 and the second detector arrangement 220, eachfibre may be identified according to above and relevant off-set valuesfor each FBG of the identified fibres are provided.

After the method step s450 a method step s460 is performed.

The method step s460 comprises the step of determining a temperaturechange course as a basis for a decision regarding how to deal with saidtemperature change. By determining said course it may be determined,e.g. by simulations/calculations/modelling, if it is necessary toperform maintenance of the platform. If it is determined thatmaintenance should be performed it may also be determined at what pointof time such measures should be taken. The decision may be taken by anysuitable means, such as the first control arrangement 231 or at aplatform management centre. In case the decision is taken externally ofthe platform temperature change course data may be provided to thedecision making unit by a suitable link (not shown).

After the method step s460 the method ends/is returned.

FIG. 5 is a diagram of one version of a device 500. The controlarrangements 233, 243 and 253 described with reference to FIG. 2 may inone version comprise the device 500. The device 500 comprises anon-volatile memory 520, a data processing unit 510 and a read/writememory 550. The non-volatile memory 520 has a first memory element 530in which a computer program, e.g. an operating system, is stored forcontrolling the function of the device 500. The device 500 furthercomprises a bus controller, a serial communication port, I/O means, anA/D converter, a time and date input and transfer unit, an event counterand an interruption controller (not depicted). The non-volatile memory520 has also a second memory element 540.

The computer program P comprises routines for determining temperaturechanges of an optical fibre 250 having Fiber Bragg Grating patternsprovided in at least one portion Portion 1 of said optical fibre 250,said optical fibre 250 being connected between a first detectorarrangement 210 and a second detector arrangement 220.

The computer program P may comprise routines for emitting light intosaid optical fibre 250 in a first direction D1 from said first detectorarrangement 210, receiving reflections from said (FBG) patterns of suchemitted light by said first detector arrangement 210, and processingsaid reflections for determining a current temperature change related tosaid optical fibre 250.

The computer program P may comprise routines for, on the basis ofpredetermined criteria, emitting light into said optical fibre 250 in anopposite, second, direction D2 from said second detector arrangement220, receiving reflections from said patterns of such emitted light bysaid second detector arrangement 220, and processing said reflectionsfor determining a current temperature change related to said opticalfibre 250.

The computer program P may comprise routines for controlling emission oflight from said second detector arrangement 220 if it is determined thatsaid first detector arrangement 210 is not operating properly and/or ifit is determined that a disconnection along said optical fibre 250 is athand

The computer program P may comprise routines for controlling operationof only one of said first detector arrangement 210 and said seconddetector arrangement 220. The computer program P may comprise routinesfor controlling operation, in an alternating manner, of said firstdetector arrangement 210 and said second detector arrangement 220. Thecomputer program P may comprise routines for controlling operation ofboth said first detector arrangement 210 and said second detectorarrangement 220 simultaneously.

The computer program P may comprise routines for determining a positionof a temperature change along said optical fibre 250 by performing acombined wavelength division multiplexing and time divisionmultiplexing.

The computer program P may comprise routines for determining atemperature change course as a basis for a decision regarding how todeal with said temperature change.

The computer program P may comprise routines for:

detecting an identity of a certain optical fibre; and

determining a predetermined off-set characteristics related to the FiberBragg Grating patterns of said certain optical fibre.

The computer program P may comprise routines for performing any of theprocess steps detailed with reference to FIG. 4a and FIG. 4b .

The program P may be stored in an executable form or in compressed formin a memory 560 and/or in a read/write memory 550.

Where it is stated that the data processing unit 510 performs a certainfunction, it means that it conducts a certain part of the program whichis stored in the memory 560 or a certain part of the program which isstored in the read/write memory 550.

The data processing device 510 can communicate with a data port 599 viaa data bus 515. The non-volatile memory 520 is intended forcommunication with the data processing unit 510 via a data bus 512. Theseparate memory 560 is intended to communicate with the data processingunit via a data bus 511. The read/write memory 550 is arranged tocommunicate with the data processing unit 510 via a data bus 514. Thelinks L200, L210 and L220, for example, may be connected to the dataport 599 (see FIG. 2).

When data are received on the data port 599, they are stored temporarilyin the second memory element 540. When input data received have beentemporarily stored, the data processing unit 510 will be prepared toconduct code execution as described above.

Parts of the methods herein described may be conducted by the device 500by means of the data processing unit 510 which runs the program storedin the memory 560 or the read/write memory 550. When the device 500 runsthe program, method steps and process steps herein described areexecuted.

The foregoing description of the preferred embodiments of the presentinvention is provided for illustrative and descriptive purposes. It isnot intended to be exhaustive, nor to limit the invention to thevariants described. Many modifications and variations will obviouslysuggest themselves to one skilled in the art. The embodiments have beenchosen and described in order to best explain the principles of theinvention and their practical applications and thereby make it possiblefor one skilled in the art to understand the invention for differentembodiments and with the various modifications appropriate to theintended use.

1. A method for determining strain changes of an optical fibre (250)having Fiber Bragg Grating (FBG) patterns provided in at least oneportion (Portion 1) of said optical fibre (250), said optical fibre(250) being connected between a first detector arrangement (210) and asecond detector arrangement (220), wherein said first detectorarrangement (210) comprises a first light emitting device (231), a firstlight detecting device (232) and a first control arrangement (233; 500),wherein said second detector arrangement (220) comprises a second lightemitting device (241), a second light detecting device (242) and asecond control arrangement (243; 500), the optical fibre (250) comprisesa core and a casing, wherein the length of the core of the optical fibre(250) is longer than the casing of the optical fibre (250); the methodcomprising the steps of: emitting (s410) light into said optical fibre(250) in a first direction (D1) from said first detector arrangement(210), receiving reflections from said FBG] patterns of such emittedlight by said first detector arrangement (210), and processing saidreflections for determining a current strain change related to saidoptical fibre (250); on the basis of predetermined criteria, emitting(s440) light into said optical fibre (250) in an opposite, second,direction (D2) from said second detector arrangement (220), receivingreflections from said FBG patterns of such emitted light by said seconddetector arrangement (220), and processing said reflections fordetermining a current strain change related to said optical fibre (250).2. The method according to claim 1, comprising the step of: emitting(s420) light from said second detector arrangement (220) if it isdetermined that said first detector arrangement (210) is not operatingproperly and/or if it is determined that a disconnection along saidoptical fibre (250) is at hand.
 3. The method according to claim 1,comprising the step of: operating (s430) only one of said first detectorarrangement (210) and said second detector arrangement (220); oroperating (s430), in an alternating manner, said first detectorarrangement (210) and said second detector arrangement (220); oroperating (s430) both said first detector arrangement (210) and saidsecond detector arrangement (220) simultaneously.
 4. The methodaccording to claim 1, comprising the step of: determining (s450) aposition of a strain change along said optical fibre (250) by performinga combined wavelength division multiplexing and time divisionmultiplexing.
 5. The method according to claim 1, comprising the stepof: determining a strain change course as a basis for a decisionregarding how to deal with said strain change.
 6. The method accordingto claim 1, comprising the step of: providing a number of optical fibreshaving Fiber Bragg Grating (FBG) patterns provided in at least oneportion of each of said optical fibres, said optical fibres beingconnected between the first detector arrangement (210) and the seconddetector arrangement (220).
 7. The method according to claim 6,comprising the steps of: detecting (s450) an identity of a certainoptical fibre; and determining (s450) a predetermined off-setcharacteristics related to the Fiber Bragg Grating (FBG) patterns ofsaid certain optical fibre (250).
 8. A system (289) for determiningstrain changes of an optical fibre (250) having Fiber Bragg Grating(FBG) patterns provided in at least one portion (Portion 1) of saidoptical fibre (250), the system comprising: a first detector arrangement(210) and a second detector arrangement (220) wherein said firstdetector arrangement (210) and second detector arrangement (220) beingconnected by said optical fibre (250); said first detector arrangement(210) comprises a first light emitting device (231), a first lightdetecting device (232) and a first control arrangement (233; 500); saidfirst light emitting device (231) being arranged for emitting light intosaid optical fibre (250) in a first direction (D1) from said firstdetector arrangement (210), said first light detecting device (232)being arranged for receiving reflections from said FBG patterns of suchemitted light by said first detector arrangement (210), and said firstcontrol arrangement (233; 500) being arranged for processing saidreflections for determining a current strain change related to saidoptical fibre (250); said second detector arrangement (220) comprises asecond light emitting device (241), a second light detecting device(242) and a second control arrangement (243; 500); said second lightemitting device (241) being arranged for, on the basis of predeterminedcriteria, emitting light into said optical fibre (250) in an opposite,second, direction (D2) from said second detector arrangement (220), saidsecond light detecting device (242) being arranged for receivingreflections from said FBG patterns of such emitted light by said seconddetector arrangement (220), and said second control arrangement (243;500) being arranged for processing said reflections for determining acurrent strain change related to said optical fibre (250); the opticalfibre (250) comprises a core and a casing, wherein the length of thecore of the optical fibre (250) is longer than the casing of the opticalfibre (250).
 9. The system according to claim 8, comprising: said secondlight emitting device (241) being arranged for emitting light from saidsecond detector arrangement (220) if it is determined that said firstdetector arrangement (210) is not operating properly and/or if it isdetermined that a disconnection along said optical fibre (250) is athand.
 10. The system according to claim 8, comprising: controlarrangements (233; 243; 253) for operating said first detectorarrangement (210) and said second detector arrangement (220) in such away that: only one of said first detector arrangement (210) and saidsecond detector arrangement (220) is operating; or said first detectorarrangement (210) and said second detector arrangement (220) areoperating in an in an alternating manner; or said first detectorarrangement (210) and said second detector arrangement (220) areoperating simultaneously.
 11. The system according to claim 8,comprising: control arrangements (233; 243; 253; 500) being arranged fordetermining a position of a strain change along said optical fibre (250)by performing a combined wavelength division multiplexing and timedivision multiplexing.
 12. The system according to claim 8, comprising:control arrangements (233; 243; 253; 500) being arranged for determininga strain change course as a basis for a decision regarding how to dealwith said strain change.
 13. The system according to claim 8,comprising: a number of optical fibres having Fiber Bragg Grating (FBG)patterns provided in at least one portion (Portion 1) of each of saidoptical fibres, wherein said number of optical fibres are arranged to beconnected between the first detector arrangement (210) and the seconddetector arrangement (220).
 14. The system according to claim 8,comprising: detector arrangements (210; 220) being arranged fordetecting an identity of a certain optical fibre; and controlarrangements (233; 243; 253; 500) being arranged for determining apredetermined off-set characteristics related to the Fiber Bragg Grating(FBG) patterns of said certain optical fibre.
 15. A platform (100)comprising a system (289) according to claim
 8. 17. A non-transitorycomputer-readable storage medium comprising instructions which, whenexecuted by a computer (200; 210), cause the computer (200; 210) tocarry out the method according to claim
 1. 18. An aircraft comprising asystem (289) according to claim 8.